Lex Luthor Comes to 'Supergirl' in March 17's "O Brother Where Art Thou?"

The CW has released the official synopsis for "O Brother, Where Art Thou?," the March 17 episode of Supergirl which will introduced Jon Cryer as Lex Luthor.

In the episode, Lex -- who has previously been identified as having been sent to prison by Superman -- shows up in National City, apparently having been released due to poor health. His agenda? Recruiting his sister Lena (Katie McGrath) to help him cure it.

While there is no specific indication as to what it is that is killing Lex, the comics may offer one potentially promising idea: Kryptonite poisoning.

While humans do not have the same immediate reaction to Kryptonite that Kryptonians do, the radiation from the alloy can cause harm and even death when people are exposed to it over long periods of time. In the post-Crisis on Infinite Earths continuity, Luthor regularly wore a Kryptonite ring to keep the Man of Steel at bay -- until it poisoned him, first forcing his hand to be amputated and ultimately taking his life.

(Kind of. He would later clone himself a new body and put his brain into it, masquerading as his own son for a time because comics.)

The Kryptonite poisoning angle would make sense, given that Lena has picked up on and improved Lex's own synthetic Kryptonite research. That would make her a potential expert in the field of its properties and one of a very small number of people who could potentially help him recover from the lingering effects of long-term Kryptonite poisoning.

...Of course, if Lex Luthor comes to you asking for help with Kryptonite, do you help?

You can see the official synopsis below.

JON CRYER GUEST STARS AS ICONIC DC COMICS' VILLAIN LEX LUTHOR

Secretly furloughed from prison due to failing health, Lex Luthor (guest star Jon Cryer) visits his sister, Lena (Katie McGrath), to seek her help finding a cure. Savvy as ever, Lena is suspicious of Lex's motives but when she's faced with a life and death situation, she must decide how she truly feels about her brother.

Meanwhile, Supergirl (Melissa Benoist) and J'onn (David Harewood) face off against Manchester Black (guest star David Ajala). James' sister Kelly (guest star Azie Tesfai) comes to town.

Tawnia Mckiernan directed the episode written by Derek Simon & Nicki Holcomb.

Supergirl airs on Sunday nights at 8 p.m. ET/PT, before episodes of Charmed on The CW. "O Brother Where Art Thou?" will premiere on March 17.